1. Field of the Invention
The present invention relates to air-cooled chillers. More particularly, the present invention relates to a chiller with multiple refrigerant circuits, wherein an active circuit uses airflow created by a condenser fan of an inactive circuit.
2. Description of Related Art
Chiller systems usually include at least one refrigerant circuit for providing a cooling effect. A typical refrigerant circuit comprises a compressor for compressing and forcing refrigerant through the circuit, a condenser for condensing compressed refrigerant and expelling waste heat, an expansion device for reducing the temperature of the refrigerant through expansion, and an evaporator that enables the refrigerant inside to cool an external fluid, such as air or water.
Some chiller systems include multiple refrigerant circuits that can be selectively activated for meeting a range of cooling demands. For high cooling demands, all of the circuits may be activated. Under certain low load conditions, some circuits, or selected components thereof, may be de-energized.
For instance, a chiller may include two refrigerant circuits, each having their own compressor, condenser, expansion device and evaporator: similar to the chiller disclosed in U.S. Pat. No. 4,506,516. At times, both circuits may work together to provide a maximum combined cooling effect. At moderate cooling loads, only one of the circuits may need to operate. If the load becomes even lighter, the capacity of the one circuit that is operating may itself need to be reduced. To reduce the capacity of a single refrigerant circuit, its condenser may be provided with several fans that can be individually de-energized to incrementally reduce the airflow across the condenser, as disclosed in U.S. Pat. Nos. 5,138,844 and 5,067,560.
However, under certain low ambient temperature conditions, even a single fan may provide too much airflow across the condenser. This may require the fan to cycle on and off excessively, which in turn can adversely affect load control, expansion valve positioning, and the quality of vapor entering the compressor. To avoid such problems, the last operating fan can be made smaller than the rest (e.g., U.S. Pat. No. 4,628,701), or the last operating fan can be driven by an inverter that reduces the speed of the fan. Unfortunately, inverters can be expensive, and a smaller fan can limit a chiller""s maximum capacity. Moreover, even a smaller fan may provide too much airflow under certain conditions.
It is an object of the present invention to provide a simple, low-cost alternative to operating a multi-circuit chiller at low ambient temperature conditions.
Another object of the invention is to use a fan of an inactive condenser to cool a condenser of an active refrigerant circuit.
Another object pertaining to using a fan of an inactive condenser to cool an active condenser is to force appreciably less air across the active condenser than across the inactive condenser.
A still further object is to use an air duct to provide a restricted airflow path from one condenser of an active refrigerant circuit to another condenser of an inactive circuit.
One or more of these objects are provided by a chiller system that includes at least two refrigerant circuits. In a low ambient temperature condition, one circuit is active while the other is inactive. A condenser fan associated with the inactive circuit is energized to draw air across a condenser of the active circuit.
The present invention provides a chiller system. The chiller system comprises a first refrigerant circuit that includes an energized compressor and a first condenser; a second refrigerant circuit that includes a de-energized compressor and a second condenser; a de-energized fan adjacent the first condenser such that the de-energized fan is closer to the first condenser than the second condenser; and an energized fan adjacent the second condenser such that the energized fan is closer to the second condenser than the first condenser.
The present invention also provides a chiller system selectively operable in a low ambient temperature mode. The chiller comprises a first refrigerant circuit that includes a first compressor and a first condenser; a second refrigerant circuit that includes a second compressor and a second condenser; a first fan adjacent the first condenser such that the first fan is closer to the first condenser than the second condenser; a second fan adjacent the second condenser such that the second fan is closer to the second condenser than the first condenser; an air duct that places the first condenser in air communication with the second condenser; and a control operatively connected to the first compressor, the second compressor, the first fan and the second fan. The control energizes the first compressor, energizes the second fan, de-energizes the second compressor, and de-energizes the first fan to allow the second fan to draw air in series across the first condenser, through the air duct, and across the second condenser, thereby placing the chiller system in the low ambient temperature mode of operation.
The present invention further provides a chiller system. The chiller system comprises a first chiller module comprising a first refrigerant circuit and a first pair of condenser fans, and a second chiller module comprising a second refrigerant circuit and a second pair of condenser fans. The first refrigerant circuit includes, in series flow relationship with each other, a first compressor, a first condenser, a first expansion device, and a first evaporator. The first condenser defines a first condenser plenum, the first pair of condenser fans are adjacent the first condenser, and the first refrigerant circuit contains a first charge of refrigerant. The second refrigerant circuit includes, in series flow relationship with each other, a second compressor, a second condenser, a second expansion device, and a second evaporator. The second condenser defines a second condenser plenum, the second pair of condenser fans are adjacent the second condenser, and the second refrigerant circuit contains a second charge of refrigerant separate from the first charge of refrigerant. The chiller system also comprises an air duct connecting the first condenser plenum in fluid communication with the second condenser plenum; and a control operatively connected to the first compressor, the first pair of condenser fans, the second compressor, and the second pair of condenser fans. The control energizes the first compressor, energizes one fan of the second pair of condenser fans, de-energizes another fan of the second pair of condenser fans, and de-energizes the first pair of condenser fans, thereby placing the chiller system in a low ambient temperature mode of operation wherein the one fan draws air in series across the first condenser, through the first condenser plenum, through the air duct, through the second condenser plenum, and across the second condenser.
The present invention additionally provides a method of operating a chiller system. The method comprises forcing a first charge of refrigerant to flow in series through a first compressor and a first condenser; inhibiting a second charge of refrigerant from flowing in series through a second compressor and a second condenser; and forcing more air across the second condenser than across the first condenser.
The present invention moreover provides a chiller system. The system comprises a first compressor; a second compressor; a first condenser in operative association with the first compressor; a second condenser in operative association with the second compressor; elements forcing a first charge of refrigerant to flow in series through a first compressor and a first condenser; a device inhibiting a second charge of refrigerant from flowing in series through a second compressor and a second condenser; and a device forcing more air across the second condenser than across the first condenser.